In the production of a slide fastener a pair of coupling elements typically formed as helicoidal chains are secured to the edges of respective tapes and are interleaved. The coupling elements are then punched out at longitudinally spaced locations. Then the end stop members and slider are mounted on the coupling elements and the tape assemblies are cut at the punch locations to form individual slide fasteners.
The tape assembly comprising the tapes with the interleaved coupling elements is moved in steps through a gapping machine of the type described in German patent document No. 2,360,947 filed by Kihei Takahashi with a claim to a Japanese priority date of Dec. 6, 1972. Here the coupling elements are engaged by upstream and downstream elements that position them underneath a punch that moves down to cut the heads off the interleaved turns of the coupling elements. The half turns left on the tapes are then stripped therefrom by means of laterally effective rakes.
It is essential that entire coupling heads be removed, that no partial heads be left on the tapes. Thus this German patent document teaches that the positioning device comprises upstream and downstream gripper fingers that are pushed down onto the coupling elements, then pushed together to longitudinally compact and compress the tape assembly. The intent of such a procedure is to compress the coupling chains in such a manner that a whole number of heads are positioned under the punch and therefore no partial heads are left.
In this arrangement, however, the compressibility of the coupling elements and the tapes carrying them can vary considerably. The result is, of course, nonuniform compression and the occasional chopping of coupling heads in half, spoiling the entire fastener.
Another disadvantage results from the way the grippers move vertically down onto the coupling elements and then move longitudinally toward each other. When the pins or fingers of the grippers do not engage between turns of the coupling elements but instead land directly atop the turns of the coils, the grippers can slip slightly when pushed together, resulting in a misfeed that can produce an improperly chopped chain.